﻿using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;

namespace Problem008
{
    class Program
    {
        private const int SUBSTRING_LENGTH = 5;

        private const string number =
            "73167176531330624919225119674426574742355349194934"
            + "96983520312774506326239578318016984801869478851843"
            + "85861560789112949495459501737958331952853208805511"
            + "12540698747158523863050715693290963295227443043557"
            + "66896648950445244523161731856403098711121722383113"
            + "62229893423380308135336276614282806444486645238749"
            + "30358907296290491560440772390713810515859307960866"
            + "70172427121883998797908792274921901699720888093776"
            + "65727333001053367881220235421809751254540594752243"
            + "52584907711670556013604839586446706324415722155397"
            + "53697817977846174064955149290862569321978468622482"
            + "83972241375657056057490261407972968652414535100474"
            + "82166370484403199890008895243450658541227588666881"
            + "16427171479924442928230863465674813919123162824586"
            + "17866458359124566529476545682848912883142607690042"
            + "24219022671055626321111109370544217506941658960408"
            + "07198403850962455444362981230987879927244284909188"
            + "84580156166097919133875499200524063689912560717606"
            + "05886116467109405077541002256983155200055935729725"
            + "71636269561882670428252483600823257530420752963450";

        private static readonly Func<string, long> ProductOfDigits = x =>
                                   {
                                       var chars = x.ToCharArray();
                                       var product = 1;

                                       foreach (var c in chars)
                                       {
                                           product *= Int32.Parse(c.ToString());
                                       }

                                       return product;
                                   };

        static void Main()
        {
            var stopwatch = new Stopwatch();

            stopwatch.Start();
            Console.WriteLine(DetermineProductOfConsecutiveDigits().Max());
            stopwatch.Stop();

            Console.WriteLine("Execution time: {0}ms", stopwatch.ElapsedMilliseconds);

            Console.ReadKey();
        }

        private static IEnumerable<long> DetermineProductOfConsecutiveDigits()
        {
            for (var index = 0; index + SUBSTRING_LENGTH < number.Length - 1; index++)
            {
                var fiveDigits = number.Substring(index, SUBSTRING_LENGTH);
                yield return ProductOfDigits(fiveDigits);
            }
        }
    }
}
